ServerRpcHandler中的Vaadin NPE

时间：2014-11-01 14:57:05

标签： java nullpointerexception vaadin

本周我开始使用Vaadin，从此给我留下了深刻的印象。但是，我遇到了一个我无法解决的问题。基本上我创建了一个Web应用程序，我在其中显示Contacts（存储在我的数据库中）并将它们显示在表中。

由于我使用的是Hibernate，所以我从以下代码行开始：

    JPAContainer<Contact>contactContainer = new JPAContainer<Contact>(Contact.class);
    CachingMutableLocalEntityProvider<Contact> entityProvider = new CachingMutableLocalEntityProvider<Contact>(Contact.class, em);
    contactContainer.setEntityProvider(entityProvider);

    contactsList = new ContactsList(contactContainer);

如您所见，我将容器传递给一个名为ContactsList的类，其中构建了表等：

    table = new Table();
    table.setWidth(100, Unit.PERCENTAGE);
    table.addStyleName(ValoTheme.TABLE_BORDERLESS);
    table.addStyleName(ValoTheme.TABLE_COMPACT);
    table.setSelectable(true);
    table.setColumnCollapsingAllowed(true);

    if(container != null)
    {
        table.setContainerDataSource(this.container);
        table.setSortAscending(true);
        table.setVisibleColumns("firstName", "lastName", "telephoneNr", "gsmNr", "creationDate");
        table.setColumnHeaders(SpringUtil.getMessage("label.contacts_firstname", null), 
                                SpringUtil.getMessage("label.contacts_lastname", null), 
                                SpringUtil.getMessage("label.contacts_telephone_nr", null), 
                                SpringUtil.getMessage("label.contacts_gsm_nr", null),
                                SpringUtil.getMessage("label.contacts_creationdate", null));
    }

    table.setMultiSelect(true);
    table.setImmediate(true);

当我注释掉所有这些代码时，我的应用程序运行完美而不会崩溃（当然没有显示联系人表）但是当我尝试编译这段代码时，即使在构建了表之后调试一切也很好但是然后是NPE在课程ServerRpcHandler中抛出：

if (invocation instanceof ServerRpcMethodInvocation) {
    try {
        ServerRpcManager.applyInvocation(connector,
                 (ServerRpcMethodInvocation) invocation);
        } catch (RpcInvocationException e) {
                  manager.handleConnectorRelatedException(connector, e);
        }
} else {

此处显示完整的StackTrace：

    SEVERE: java.lang.NullPointerException
    at com.vaadin.addon.jpacontainer.provider.LocalEntityProvider.getEntityManager(LocalEntityProvider.java:215)
    at com.vaadin.addon.jpacontainer.provider.LocalEntityProvider.doGetEntityManager(LocalEntityProvider.java:226)
    at com.vaadin.addon.jpacontainer.provider.LocalEntityProvider.doGetEntityCount(LocalEntityProvider.java:510)
    at com.vaadin.addon.jpacontainer.provider.CachingSupport$FilterCacheEntry.getEntityCount(CachingSupport.java:157)
    at com.vaadin.addon.jpacontainer.provider.CachingSupport.getEntityCount(CachingSupport.java:826)
    at com.vaadin.addon.jpacontainer.provider.CachingMutableLocalEntityProvider.getEntityCount(CachingMutableLocalEntityProvider.java:130)
    at com.vaadin.addon.jpacontainer.JPAContainer.size(JPAContainer.java:912)
    at com.vaadin.ui.AbstractSelect.size(AbstractSelect.java:762)
    at com.vaadin.ui.Table.refreshRenderedCells(Table.java:1727)
    at com.vaadin.ui.Table.attach(Table.java:4298)
    at com.vaadin.server.AbstractClientConnector.attach(AbstractClientConnector.java:590)
    at com.vaadin.ui.AbstractComponent.attach(AbstractComponent.java:577)
    at com.vaadin.server.AbstractClientConnector.attach(AbstractClientConnector.java:590)
    at com.vaadin.ui.AbstractComponent.attach(AbstractComponent.java:577)
    at com.vaadin.server.AbstractClientConnector.attach(AbstractClientConnector.java:590)
    at com.vaadin.ui.AbstractComponent.attach(AbstractComponent.java:577)
    at com.vaadin.server.AbstractClientConnector.attach(AbstractClientConnector.java:590)
    at com.vaadin.ui.AbstractComponent.attach(AbstractComponent.java:577)
    at com.vaadin.server.AbstractClientConnector.attach(AbstractClientConnector.java:590)
    at com.vaadin.ui.AbstractComponent.attach(AbstractComponent.java:577)
    at com.vaadin.server.AbstractClientConnector.attach(AbstractClientConnector.java:590)
    at com.vaadin.ui.AbstractComponent.attach(AbstractComponent.java:577)
    at com.vaadin.server.AbstractClientConnector.attach(AbstractClientConnector.java:590)
    at com.vaadin.ui.AbstractComponent.attach(AbstractComponent.java:577)
    at com.vaadin.server.AbstractClientConnector.attach(AbstractClientConnector.java:590)
    at com.vaadin.ui.AbstractComponent.attach(AbstractComponent.java:577)
    at com.vaadin.server.AbstractClientConnector.attach(AbstractClientConnector.java:590)
    at com.vaadin.ui.AbstractComponent.attach(AbstractComponent.java:577)
    at com.vaadin.server.AbstractClientConnector.attach(AbstractClientConnector.java:590)
    at com.vaadin.ui.AbstractComponent.attach(AbstractComponent.java:577)
    at com.vaadin.ui.AbstractComponent.setParent(AbstractComponent.java:484)
    at com.vaadin.ui.AbstractComponentContainer.addComponent(AbstractComponentContainer.java:210)
    at com.vaadin.ui.CssLayout.addComponent(CssLayout.java:120)
    at com.vaadin.navigator.Navigator$ComponentContainerViewDisplay.showView(Navigator.java:191)
    at com.vaadin.navigator.Navigator.navigateTo(Navigator.java:568)
    at com.vaadin.navigator.Navigator.navigateTo(Navigator.java:526)
    at be.cematech.dashboard.ui.DashboardMenu$ValoMenuItemButton$1.buttonClick(DashboardMenu.java:167)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:606)
    at com.vaadin.event.ListenerMethod.receiveEvent(ListenerMethod.java:508)
    at com.vaadin.event.EventRouter.fireEvent(EventRouter.java:198)
    at com.vaadin.event.EventRouter.fireEvent(EventRouter.java:161)
    at com.vaadin.server.AbstractClientConnector.fireEvent(AbstractClientConnector.java:977)
    at com.vaadin.ui.Button.fireClick(Button.java:387)
    at com.vaadin.ui.Button$1.click(Button.java:55)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:606)
    at com.vaadin.server.ServerRpcManager.applyInvocation(ServerRpcManager.java:168)
    at com.vaadin.server.ServerRpcManager.applyInvocation(ServerRpcManager.java:118)
    at com.vaadin.server.communication.ServerRpcHandler.handleInvocations(ServerRpcHandler.java:290)
    at com.vaadin.server.communication.ServerRpcHandler.handleRpc(ServerRpcHandler.java:183)
    at com.vaadin.server.communication.UidlRequestHandler.synchronizedHandleRequest(UidlRequestHandler.java:92)
    at com.vaadin.server.SynchronizedRequestHandler.handleRequest(SynchronizedRequestHandler.java:41)
    at com.vaadin.server.VaadinService.handleRequest(VaadinService.java:1404)
    at com.vaadin.server.VaadinServlet.service(VaadinServlet.java:305)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:727)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:303)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
    at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:241)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:220)
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:122)
    at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:503)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:170)
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:103)
    at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:950)
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:116)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:421)
    at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1070)
    at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:611)
    at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:316)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
    at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
    at java.lang.Thread.run(Thread.java:745)

更新

可能有用的是，我在不同的页面上使用此ContactList，以及我有完全相同的代码行，但它能够显示表格。这是否有两个EntityManagers和/或EntityProviders访问相同的数据？

UPDATE2 

@PersistenceContext
protected EntityManager em;

1 个答案:

答案 0 :(得分：1)

根据Update2，我看到你在运行时使用注释“@PersistenceContext”检索你的EntityManager。 如果您在“CDI bean，EJB，Servlet，Servlet侦听器，Servlet过滤器或JSF ManagedBean”中使用它，则可以解决此问题。 （http://tomee.apache.org/examples-trunk/injection-of-entitymanager/README.html） 我的猜测是，在“其他页面”上，您处于注释有效的正确上下文中，而在“此”页面中则不是。 检查一下，如果是这种情况，我建议手动实例化EntityManager，例如

JPAContainerFactory.make(Contact.class, "PERSISTENCE_UNIT_NAME");

如果您在项目中使用/使用persistence.xml文件。否则，一种方法是自定义创建像

这样的EntityManagerFactory 
Persistence.createEntityManagerFactory( "persistence_unit_name", properties ).createEntityManager()

其中properties是一个持久性属性的地图，如

Map<String, String> properties = new HashMap<String, String>();
properties.put(JDBC_DRIVER, this.jdbcDriver);
properties.put(JDBC_URL, this.url);
properties.put(JDBC_USER, this.username);
properties.put(JDBC_PASSWORD, this.password);

// Configure logging. FINE ensures all SQL is shown
properties.put(LOGGING_LEVEL, "FINE");  
return properties;

像这样的EntityManager的好处是，无论何时你在你的应用程序中，你都可以准备好它。 欢呼声。

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